Chlamydia trachomatis is the most commonly sexually transmitted pathogen in the United States and it is known to cause trachoma, conjunctivitis, pneumonia of the newborn and genital infections. The development of a monoclonal antibody for C. trachomatis has enabled us to screen large numbers of individuals for C. trachomatis by examining smears of genital secretions on slides stained with monoclonal antibody. A total of 1,080 patients were screened for C. trachomatis infection. The overall prevalence rate was 15.3% and the sensitivity and specificity of the direct monoclonal tests compared to culture was 88.7% and 98.5% respectively. Future aspects of this work will determine the sensitivity and specificity of this assay in detecting C. trachomatis infection in other physical sites and populations, such as newborn conjunctivitis in the U.S. and Africa, rectal infections in homosexual men, and low risk populations such as family planning clinics. In order to further study the immunopathogenesis and efficacy of therapeutic regimens for C. trachomatis, we established acute fallopian tube infection (salpingitis) in 10 cynolomogus monkeys by intratubal inoculation with C. trachomatis. Similarly, we have also established rectal infections in primates with C. trachomatis which mimic granulomatous colitis in man both clinically and histopathologically. Intratubal and intrarectal cultures remain positive in these monkeys for C. trachomatis for six weeks post inoculation. Serial histologic examination of fallopian tube and rectal tissue demonstrate a mild acute polymorphonuclear response followed by mononuclear infiltration of the submucosa and mucosa by day 21 post inoculation. Reinoculation induces a prompt inflammatory response which consists primarily of polymorphonuclear cells and mononuclear cells. The presence of C. trachomatis was demonstrated in secretory cells by immunofluoresence and immunoperoxidase staining with monoclonal antibody to C. trachomatis. These animal studies provide a unique model to examine in detail the immunopathogenesis of chlamydial infection. Further studies will emphasize the effect of infection on mucosal and systemic immune responses.